The present invention relates to optical apparatus including mirrors, and to associated methods of manufacture and operation of such apparatus. Embodiments of the present invention are particularly suitable for, but not limited to, application in optical telescopes, particularly those telescopes launched into space.
Optical telescopes can increase the apparent angular size of distant objects, as well as the apparent brightness of such objects. Telescopes utilise one or more curved optical elements (e.g. lenses or mirrors) to gather light or other electromagnetic radiation, and bring that light/radiation to a focus, where the image can be observed, photographed or otherwise captured e.g. by a two-dimensional image sensor. Optical telescopes can be used for astronomy, and can also be used in many non-astronomical instruments including theodolites, transits, spotting scopes, monoculars, binoculars, camera lenses and spyglasses.
In order for the telescope to provide optimal performance, it is critical that the optical elements are correctly positioned, to at least within predetermined tolerances. Many telescopes will experience forces during transportation or operation, such as vibrations, accelerations, or impacts due to being dropped, which could potentially result in the misalignment of the optical elements. Perhaps the most extreme example of such a force is the acceleration experienced by telescopes for use in space, as they are launched from the earth by rocket.
Other factors, including environmental factors, will affect the mechanical stability of optical apparatus such as telescopes, and hence affect the relative alignment of the optical elements within the apparatus. For example, material properties will undergo changes depending upon the environment in which they are located e.g. in a vacuum environment outgassing can occur, whilst in other environments materials may absorb gases from the environment. The materials within the optical apparatus can also be affected by environmental temperatures. Material properties may also alter over time due to temperature effects, e.g. due to the materials experiencing relatively high or low temperatures, or cycles of temperatures. Materials will often expand or contract as a function of temperature, potentially resulting in changes in the relative positions of optical elements within the optical apparatus. Equally, different portions of the apparatus may experience different temperatures (i.e. a temperature gradient may be set up across the apparatus) that could also result in relative movement (and hence misalignment) of the optical elements.
It is particularly critical in space telescopes that the optimum alignment of the optical elements is maintained, due to the difficulties and prohibitive cost associated with manually re-aligning the optical elements once the telescope is in space.
In order to prevent misalignment of the optical elements within such telescopes, extremely rigid supports, such as struts, are used to fix the optical elements into position. Disadvantageously, providing such rigid support structures results in an increase in weight of the telescope. This is particularly disadvantageous for space telescopes, due to the prohibitive cost associated with launching heavy objects into space.
It is an aim of embodiments of the present invention to address one or more problems of the prior art, whether referred to herein or otherwise. It is an aim of particular embodiments of the present invention to provide an approved optical mirror system which may be used in space telescopes.